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ACS Chem Biol. 2017 May 19;12(5):1245-1256. doi: 10.1021/acschembio.6b01060. Epub 2017 Mar 20.

A Chemical Probe Strategy for Interrogating Inhibitor Selectivity Across the MEK Kinase Family.

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Department of Chemistry, Northwestern University , Evanston, 60208, Illinois, United States.
Center for Molecular Innovation and Drug Discovery, Northwestern University , 2145 Sheridan Rd, Evanston, Illinois 60208, United States.
Chemistry of Life Processes Institute, Northwestern University , 2145 Sheridan Rd, Evanston, Illinois 60208, United States.
Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago , 900 S Ashland Ave, Chicago, Illinois 60607, United States.
Knight Cancer Institute, Oregon Health & Science University , 3181 S.W. Sam Jackson Park Rd., Portland, Oregon 97239, United States.
Department of Pharmacology, Feinberg School of Medicine, Northwestern University , Chicago, Illinois 60611, United States.


MEK4 is an upstream kinase in MAPK signaling pathways where it phosphorylates p38 MAPK and JNK in response to mitogenic and cellular stress queues. MEK4 is overexpressed and induces metastasis in advanced prostate cancer lesions. However, the value of MEK4 as an oncology target has not been pharmacologically validated because selective chemical probes targeting MEK4 have not been developed. Despite a high level of sequence homology in the ATP-binding site, most reported MEK inhibitors are selective for MEK1/2 and display reduced potency toward other MEKs. Here, we present the first functional and binding selectivity-profiling platform of the MEK family. We applied the platform to profile a set of known kinase inhibitors and used the results to develop an in silico approach for small molecule docking against MEK proteins. The docking studies identified molecular features of the ligands and corresponding amino acids in MEK proteins responsible for high affinity binding versus those driving selectivity. WaterLOGSY and saturation transfer difference (STD) NMR spectroscopy techniques were utilized to understand the binding modes of active compounds. Further minor synthetic manipulations provide a proof of concept by showing how information gained through this platform can be utilized to perturb selectivity across the MEK family. This inhibitor-based approach pinpoints key features governing MEK family selectivity and clarifies empirical selectivity profiles for a set of kinase inhibitors. Going forward, the platform provides a rationale for facilitating the development of MEK-selective inhibitors, particularly MEK4 selective inhibitors, and repurposing of kinase inhibitors for probing the structural selectivity of isoforms.

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